Interesting. Many people who can’t fall asleep actually have different circadian rhythms and are natural night owls. The problem for this group seems like insomnia when it’s actually having to get up too early. If you use an alarm clock to wake up, your sleep times may not match your innate circadian rhythm. In that case, how can you change your life to fit your natural circadian rhythm? Trying to fight it only leads to chronic sleep deprivation.
According to science of chronotypes there are not too much natural night owls in population, most of them night owl because of social / technological influence. For example you can check this paper which states “we find 40% early, 44% intermediate and only 16% late chronotypes.”
Agree, but there is a lot of other reasons for insomnia.
I dont use alarms. I’ve measured my circadian rhythm and it seems to be synchronized with my bedtime start: around 22:00 my body temperature drops and my sleep is initiated and it start to rise at about 5:00 and waking me up.
I think the best timing for alarm is 30-60 mins after your usual waking time 
I’m not using alarm, but if was forced to, i’ll shift my bedtime start to (alarm time - 8.5 hours) to wake up naturally. Also i think it good to shift breakfast and dinner to match that schedule (no eat 3-4h before bedtime and wait 1-2h after waking up).
Circadian rhythm can be shifted, just give it a some time. Most of thing which is matter for suprachiasmatic nucleus (which syncs rhythms) is a bright light sensed by melanopsin containing cells in retina. If you fly from EU to US, just give it some time and rhythm will sync after few days/weeks. If you shift your schedule for 1-2 hours - just keep it strict and rhythm will shift after few days. Important thing is to setup your bedtime for a 8-9-10 hours prior alarm, to wake naturally most of days. Anyway your brain clock isnt precise to 24h and are syncing everyday with bright light and other external factors.
Most of problems came when someone try to sleep at strict schedule, like 23:00 and having bright light at 22:30 which disrupts and shift rhythm and cause long sleep latency.
Having strict bedtime schedule and optimizing daily/screentime activities seems to be best way not to fight with biological clocks
In my experiment i’ve tried to find optimal bedtime for my current external factors (sunset/sunrise/meal timing) and habitual screentime. If some of factors will change i’m assuming a changes in optimal bedtime.
I would recommend to read Matthew Walker’s book “Why we sleep” - some of the mechanisms are explained there and provides useful info supported by science.
I read the book. It revitalized my career and life. The 44% intermediate group are often sleep deprived by what’s becoming known in the literature as social jetlag.
I am in that 44%. My brain wakes naturally at 7:30 AM. However, for 34 years I had to get up at 6 AM or earlier. I have patients in the 44 % who start working at 5:30 AM. They try to go to sleep at 9 PM but can’t so they say they have trouble sleeping. They sleep fine. They just have to get up too early for their circadian rhythm.
BTW, there is a 75% increase in the incidence of type 2 diabetes in patients whose social obligations shift their sleep time 2 hours from their genetic circadian rhythm.
You are correct, we adjust to different time zones, but it’s not because we change our circadian rhythm. We’re merely adapting to the change in sunlit hours.
Suprachiasmatic nucleus is a master regulator for circadian rhythm
The primary circadian clock in mammals is located in the suprachiasmatic nucleus (or nuclei) (SCN), a pair of distinct groups of cells located in the hypothalamus.
To be more correcly, yes, we arent changing the actual circadian cycle duration, but we shifting the start of circadian cycle. Changing external factors (light/dark) affects melanopsin - SCN pathway and regulate circadian clock.
I think it doesn’t affect that much.